ABSTRACT

Amphetamine-like stimulants are commonly used to treat sleepiness in narcolepsy. These compounds have little effect on rapid eye movement (REM) sleep-related symptoms such as cataplexy, and antidepressants (monoamine uptake inhibitors) are usually required to treat these symptoms. Although amphetamine-like stimulants and antidepressants enhance monoaminergic transmission, these compounds are non-selective for each monoamine, and the exact mechanisms mediating how these compounds induce wakefulness and modulate REM sleep are not known. In order to evaluate the relative importance of dopaminergic and noradrenergic transmission in the mediation of these effects, five dopamine (DA) uptake inhibitors (mazindol, GBR-12909, bupropion, nomifensine and amineptine), two norepinephrine (NE) uptake inhibitors (nisoxetine and desipramine), d-amphetamine, and modafinil, a non-amphetamine stimulant, were tested in control and narcoleptic canines. All stimulants and dopaminergic uptake inhibitors were found to dose-dependently increase wakefulness in control and narcoleptic animals. The in vivo potencies of DA uptake inhibitors and modafinil on wake significantly correlated with their in vitro affinities to the DA and not the NE transporter. DA uptake inhibitors also moderately reduced REM sleep, but this effect was most likely secondary to slow wave sleep (SWS) suppression, since selective DA uptake inhibitors reduced both REM sleep and SWS proportionally. In contrast, selective NE uptake inhibitors had little effect on wakefulness, but potently reduced REM sleep. These results suggest that presynaptic activation of DA transmission is critical for the pharmacological control of wakefulness, while that of the NE system is critical for REM sleep regulation. Our results also suggest that presynaptic activation of DA transmission is a key pharmacological property mediating the wake-promoting effects of currently available CNS stimulants.